Fluorine-containing copolymers, obtained by copolymerization of the perfluoroalkyl compound with other copolymerizable vinyl monomers, have been known to be very useful as low-energy surface modifiers in various forms hitherto. But it is known that perfluoroalkyl compounds show poor adhesiveness due to the extremely low-energy surface characteristics with various substrates like fiber, plastic, rubber, ceramic and metal etc.
Therefore to improve the adhesiveness, comonomers have been used which have relatively high surface energy with the affinity or may be adhered by reaction to the substrates.
However, in case of random copolymers, the perfluoroalkyl compound and comonomers are resided in the backbone concurrently, thus show the mixed surface properties of the two monomers; Namely, the low-energy modification characteristics from the perfluoroalkyl compound is damaged by high surface energy comonomer, and the surface modification effect of the copolymer is reduced. Therefore, when the random copolymer is used tor low-energy, surface modification of substrates, excessive amounts of high-priced perfluoroalkyl compound should be used in order to reduce the surface energy of the substrate to the desired level. And manufacturing costs of the random copolymer are deemed to be high compared with the performances.
Recently, a graft type copolymer was synthesized using oligomer of perfluoroalkyl compound as branched chains and other comonomers as a backbone by solution or emulsion polymerization. And the graft copolymers have been used as a fluorine-containing surface modifier (Japanese Patent unexamined publication Soh 54-137489 and Soh 56-163183).
However, in case of forementioned method, an high surface energy group from the initiator is attached in the fluorinated oligomer which has so small molecular weight (degree of polymerization: about 10), and the low-energy surface properties of perfluoroalkyl group is hindered by initiator group. Hence the surface modification performance is reduced.
Furthermore, since the homopolymer of perfluoroalkyl compound as a branched chain has lower degree of polymerization, its mechanical properties may be suspected.
The inventor et al. has made their intensive studies for several years on new fluorine-containing surface modifier that has improved surface properties, surface modification effect and compatibility with substrates. As the results, the fluorine-containing graft copolymer is synthesized the emulsion copolymerization of a perfluoroalkyl compound and a macromonomer that has only high molecular weight perfluorinated segments in the backbone and shows an affinity of a branched chain to the substrates, respectively.